Channel electrode microdisc

For many mechanisms, the steady-state Eia or N tt value is a function of just one or two dimensionless parameters. If simulations are used to generate the working curve (or surface) to a sufficiently high resolution, the experimental response may be interpolated for intermediate values without the need for further simulation. A free data analysis service has been set up (Alden and Compton, 1998) via the World-Wide-Web (htttp //physchem.ox.ac.uk 8000/wwwda/) based on this method. As new simulations are developed (e.g. for wall jet electrodes), the appropriate working surfaces are simulated and added to the system. It currently supports spherical, microdisc, rotating disc, channel and channel microband electrodes at which E, EC, EC2, ECE, EC2E, DISP 1, DISP 2 and EC processes may be analysed. 

Most of the practical electrode geometries (microdisc, microband, channel, wall jet) require simulation of two spatial dimensions. Although a few early simulations used a simple explicit method (Britz, 1988), its relative inefficiency is compounded in multiple dimensions. Two ways of adding some implicit character to multidimensional simulations have been adopted ... 

The ADI method has also been apphed to convective-diffusion problems to assess the influence of convective transport on the voltammetric response of microdisc electrodes [38] in channel cells. The convective component may be routinely introduced to Eq. (28) in an analogous manner to that noted for the EFD Eq. (18). The three-dimensional transport problem was addressed in an analogous manner to the two-dimensional problem by splitting each full time increment into three time-steps of one third, to allow the x, y, and z directions to be solved implicitly. 

SECM associated with scanning ion conductance microscopy (SICM) requires a double tip, on one side of which is a conventional microdisc electrode and on the other side is a narrow pipette filled with electrolyte and an electrode that measures ionic conductance through the mouth of the pipette with respect to another electrode in the bulk solution. When the pipette mouth is within one pipette tip radius away from the sample surface, the conductance varies sufficiently to be used as a control signal to maintain the z-position of the tip during the scans, thereby affording constant-distance SECM operations [133,134]. This methodology is fast and apparently less-challenging to implement than shear force SECM, but it requires the fabrication of double-barrel tips in which one channel is left empty and the other is filled with a conventional microdisc. 

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